Guinea pigs!

Does anyone else with Guinea pigs have this problem? Every time I clean out his cage, a day or two later it's completely awful and disgusting again. This is the first Guinea pig I've had. I've had him since February. It's like as soon as I turn around there's a huge wet pile or it smells awful when I'm cleaning it literally nonstop. Is this just a normal thing that happens when you have Guinea pigs? He has a liter box and he has regular Guinea pig food, and sometimes I give him some vegetables. Celery or lettuce, carrots. His cage isn't huge, but is definitely a Decent size for him. Especially when he's out of his cage a lot. Any tips? I don't know if I'm doing something wrong.